The performance of regional anaesthesia is a first-line anaesthesia option. The object of any regional blocking technique is to deposit the sufficient volume and concentration of the local anaesthetic as close as possible to the nerves to be blocked. Blocking of peripheral or plexus nerves is used in surgical anaesthesia and to provide adequate postoperative analgesia to the patient with minimum side effects, as well as in the treatment of various chronological pathologies.
The regional techniques known in the current state of the art are based on surface anatomy landmarks, i.e. on “blind” methods for locating nerve structures, aided by the appearance of “clicks”, parasthesias, etc. At present, through advances in technology, more precise techniques such as neurostimulation and ultrasonography are applied, representing a current nerve location and identification alternative which has displaced classical techniques.
In general, the election of a certain nerve location technique will depend on personal preference, the anaesthesiologist's experience and the possibilities of the environment in which it is performed and of the patients themselves.
The use of a peripheral nerve stimulator or neurostimulator is a current nerve location and identification alternative which has displaced other direct classical techniques, such as parasthesias, and indirect techniques, such as “clicks”. This method aims to locate the motor component of one or several peripheral nerves through the administration of a continuous current, that stimulates the nerve by means of a Teflon-coated needle, which acts as a coating of the needle cylinder that prevents dispersion of the electric current, connected to an anode (negative), the frequency (in Hz), current (in mA) and duration (in msec) of which, according to the device, are controlled by the operator. The nerve to be stimulated remains interposed between the needle and the electrode. It is a highly widespread technique that necessarily requires the presence of an assistant for execution thereof. When the needle approximates the nerve, muscular responses are produced that the anaesthesiologist must be aware of for that block in particular, consequently performing injection of LA with the assistant's aid.
The use of ultrasound to perform regional blocks has dramatically changed this situation, reaching an increasingly ideal situation in the practice of nerve blocks. Now, not only is it possible to directly view the nerve structure to be blocked in order to deposit anaesthesia in the periphery thereof, but it is also possible to locate the adjacent structures to prevent complications such as vascular punctions or pneumothorax and, even more importantly, the distribution of the local anaesthetic around these nerve structures can be observed in real time and can be modified by repositioning the needle to achieve enhanced nerve block.
The technical problem raised in this solution arises from the real location and anatomic integration in the patient of the image shown on the ultrasound screen, the need to be familiarised with ultrasound systems and for in-depth knowledge of the underlying anatomy.
It is standard practice, during the performance of nerve block, for the anaesthesiologist to use both hands (ultrasound probe and needle), the dominant hand being that holding the needle. Once the place to deposit the LA has been chosen, the anaesthesiologist has the imperative need for an assistant or collaborator. The collaboration of an assistant who follows the anaesthesiologist's instructions with respect to the suction through a line connected to the needle and/or administration of small volumes of LA is required. This process, in addition to requiring close collaboration, is repeated throughout the performance of the technique and discrepancies and errors often occur in the administration of the local anaesthetic in terms of exact location, distribution and desired volumes.
The dynamism and flexibility of the ultrasound enables the nerve path to be traced from its origin to the distal ends thereof. This allows the plexuses and nerves to be located and blocked in any point along their path, adapting to each specific situation and personalising the technique for each specific patient.
Therefore, ultrasound offers a significant number of advantages that convert it into the perfect technique for application in regional anaesthesia, as:
A direct view of the structures is obtained.
The distribution of the local anaesthetic around the nerve is observed in real time.
The total doses of the drug (local anaesthetic) are optimised.
Safety is increased.
The aforementioned indications advised against are obviated.
It can be combined with other techniques such as neurostimulation.
The technical problem of this technique is that during the performance of the nerve block the anaesthesiologist uses both hands, although this problem has been addressed through the use of drug pumps operated by the anaesthesiologist, this system has not become widespread and continues to be an unsolved problem.
Therefore, a system that facilities or enhances the performance of the technique, improving its synchronisation and the administration of LA, is required.